1. Field of the Invention
The present invention relates to image forming apparatuses such as a copying machine and a printer.
2. Description of the Prior Art
In recent years, as a demand for a color image has been increased, a lot of electrostatic process color image forming apparatuses have been proposed and put into practice. In a typical example of the color image forming apparatuses, an electrostatic latent image is developed on an electrostatic photoreceptor provided on a rotary drum in each of, for example, four colors, that is, yellow, magenta, cyan and black colors and is transferred to paper, thereby to form a color image on the paper. The developing device in the above described color image forming apparatus must be a multicolor developing device capable of selectively developing an electrostatic latent image in, for example, the above described four colors.
Examples of the multicolor developing device conventionally known include one disclosed in Japanese Patent Laid-Open Gazette No. 148055/1990. The multicolor developing device comprises a plurality of developing mechanisms mounted on a movable frame which is moved back and forth in the vertical direction by moving means. When the movable frame is moved back and forth by the moving means, each of the developing mechanisms is selectively put in a position for development on the rotary drum to perform the developing function in any one of the above described different colors. Each of the developing mechanisms comprises a developer unit and a toner storage container for containing toner having any one of the different colors. The toner in the toner storage container is supplied to the developer unit by toner conveying means at the time of the developing function of the developing mechanism.
The above described conventional multicolor developing device has the following problems:
(1) Since the toner storage container is provided for each of the developing mechanisms mounted on the movable frame, a space is required for the toner storage container to move upward. Consequently, the capacity of the toner storage container is restrained to increase the number of times of the supply of toner to the toner storage container, and the color image forming apparatus is made large in size.
(2) Since the weight of the entire movable frame containing each of the developing mechanisms is increased, the inertia force due to the movement is increased and the the load applied on the moving means is increased. Consequently, it is very difficult to cope with higher speed, so that it takes long to switch the developing mechanisms. In addition, a large capacity motor is required for the movable frame.
(3) Since the capacity of the toner remaining in the toner storage container is changed, the load applied on the above described moving means at the time of driving and stopping the movable frame is changed, thereby to make it difficult to sufficiently ensure the precision of, for example, the positioning, the operation and the stop of each of the developing mechanisms.
On the other hand, a multicolor developing device having a toner storage container positioned above a developing mechanism for supplying toner to a developer unit through a flexible tube containing a spiral has been known. In a color image forming apparatus having the multicolor developing device, however, a space is required to dispose the toner storage container above the uppermost position to which the developer unit is moved, so that &he entire color image forming apparatus is made large in size. Moreover, a significantly useless space is formed below the toner storage container.
The applicant of the present invention has developed an image forming apparatus having a multicolor developing device shown in FIGS. 1 and 2 capable of sufficiently ensuring the capacity of a toner storage container as well as sufficiently ensuring the precision of, for example, the positioning of each of developing mechanisms while increasing the switching speed of the developing mechanism.
The details of the multicolor developing device shown in FIGS. 1 and 2 will be described in the embodiments. The multicolor developing device shown in FIGS. 1 and 2 comprises toner conveying means 40 for supplying toner to a developer unit 6 from a toner storage container 32. The toner conveying means 40 comprises a cylindrical member 44 extending upward in the vertical direction from the lower end of the toner storage container 32, a spiral roller 46 disposed in the cylindrical member 44 so as to extend along the cylindrical member 44 and so constructed as to feed the toner flowing into the cylindrical member 44 from the lower end of the toner storage container 32 to the upper end of the cylindrical member 44, and toner drop passage means 48 connecting the upper end of the cylindrical member 44 and the developer unit 6 and for supplying the toner fed to the upper end of the cylindrical member 44 to the developer unit 6.
In the multicolor developing device, such a state may occur that no toner exists in the intermediate part of the cylindrical member 44 even if the toner is supplied to the toner storage container 32, depending on the method of supplying the toner.
Some copying machine may be provided with an opening for toner supply for supplying toner to a toner storage container in its main body as well as a cover for toner supply covering the opening. In supplying toner, a user opens the cover, to supply toner to the toner storage container in the main body of the copying machine from a toner bottle. Alternatively, the user mounts a toner cartridge on the toner storage container in the main body of the copying machine, to supply toner to the toner storage container.
A rotating blade for toner supply for feeding the toner in the toner storage container toward a developer unit is generally provided in the toner storage container in the main body of the copying machine. Accordingly, when the user supplies toner during the copying operation in which the rotating blade for toner supply is driven, user's fingers may be brought into contact with the rotating blade for toner supply, which is very dangerous. Therefore, a method is considered of inhibiting the copying operation by, for example, tuning off the power supply of the copying machine when the cover is opened, as used in the copying machine of such a type conventionally well-known as to supply toner by opening a front door covering almost all of its front surface. However, this method reduces the operating efficiency of the copying machine.